This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to a Japanese Patent Application 2001-085651, filed on Mar. 23, 2001, the entire content of which is incorporated herein by reference.
This invention generally relates to a displacement sensor.
A displacement sensor is disclosed in, for example, a Japanese Patent Laid-Open Publication No. 7(1995)-22214. Referring to FIGS. 2(A) and 2(B), a slider 201 displaced by a displacement of an object to be detected is disposed so as to slide on a resistor 202. A ground (GND) terminal 205 connected to a ground (GND) 206 and an electric power source terminal 203 connected to an electric power source 204 are connected to both ends of the resistor 202, respectively. The resistor 202 includes a lower resistance layer 208 accumulated on a flat surface of a substrate 207, and an upper resistance layer 209 accumulated on the lower resistance layer 208.
According to the displacement sensor with the aforementioned structure, the lower resistance layer 208 is made of a material in which carbon black and carbon fiber 210 are dispersed in a synthetic resin. Therefore, there may be a case where an axial direction of the carbon fiber 210 resides in a direction perpendicular to the sliding direction along which the slider 201 slides. For example, as shown in FIG. 2(A), there may be a case where the axial direction of the carbon fiber 210 and the sliding direction of the slider 201 reside continuously in the same directions. Particularly, referring to FIG. 2(B), a large amount of carbon fiber 210 is contained in the lower resistance layer 208. The axial direction of the carbon fiber 210 extends in the direction perpendicular to the sliding direction of the slider 201.
Referring to FIG. 2(B), a large amount of carbon fiber 210 is found in the lower resistance layer 208 so that an irregular pattern may be formed on the lower resistance layer 208 along the sliding direction of the slider 201. As a result of this, the irregular pattern may be also formed on the upper resistance layer 209 along the sliding direction of the slider 201.
When the slider 201 slides on the upper resistance layer 209, abrasion powder is produced. The abrasion powder is deposited in concave portions formed on the upper resistance layer 209 so as to form an abrasion powder deposited portions 211. The abrasion powder deposited portions 211 (i.e., the concave portions) extend along the direction perpendicular to the sliding direction of the slider 201 on the upper resistance layer 209. Therefore, while the slider 201 slides on the abrasion powder deposited portions 211, the electric conduction between the slider 201 and the resistor 202 is disconnected or the resistance therebetween is increased. As a result of this, signal noise may be increased and detection accuracy of the displacement sensor may be deteriorated with elapse of time.
Accordingly, the above disclosed displacement sensor is still susceptible of certain improvements with respect to providing a contact-type displacement sensor for maintaining a high level of accuracy, especially with an elapse of time.
According to a variable resistor or displacement sensor disclosed in Japanese Patent Laid-Open Publications No. 8 (1996)-285516 and No. 8 (1996)-236320, and in a Japanese Utility Model Publication No. 2575538, when a rotor to which the slider is attached is inclined, the slider may undergo excessive elastic or plastic deformation due to the poor function of a protective member, i.e., a clearance formed between the slider and the resistor is located at a position apart from the slider. That is, if the rotor is rotated in an inclined condition in a state where the slider is disposed at an outer periphery of the rotor and the slider protective member is disposed at an inner periphery of the rotor and vice versa, the slider may be compressed at an amount equal to or greater than a difference between xe2x80x9ca set height of the sliderxe2x80x9d and xe2x80x9ca height of the protective memberxe2x80x9d at a certain rotational position of the rotor. This means that the protective member may not function effectively.
Accordingly, the above disclosed displacement sensors are still subjected to certain improvement with respect to supplying a protective member for assuring a clearance between a slider and a resistor.
Further, a Japanese Utility Model. Publication No. 5 (1993)-8920 discloses a structure in which a stopper for restricting the deformation of the slider is provided to the slider itself. According to the structure, however, the stopper is made of a conductive material. Therefore, when the stopper and the resistor are brought into contact with each other, the slider and the resistor may be electrically short-circuited. Further, an erroneous detection signal or a noise may be outputted.
Accordingly, the above disclosed displacement sensor is still subjected to certain improvement with respect to preventing a slider and a resistor from being electrically short-circuited.
Further, according to one of known displacement sensors or one of known variable resistors, a rotational member such as a rotor is crimped or a speed nut or a snap ring is employed as a component for rotatably supporting the rotational member in a housing and for preventing the rotational member from being removed in an axial direction. However, predetermined equipments or tools are required for crimping the rotational member. Further, the number of components for the displacement sensor or the variable resistor may be increased by adding components including speed nuts. This may lead to a cost increase.
The present invention provides a displacement sensor which is a contact-type displacement sensor for detecting a displacement of an object to be detected based on a change of a resistance value. The displacement sensor includes a resistor having a surface to be slid, a slider sliding on the surface to be slid in a predetermined direction (i.e., a predetermined direction, for example in one direction) in accordance with the displacement of the object to be detected, and an irregular pattern formed on the surface to be slid and including convex portions and concave portions continuously formed along a direction crossing or perpendicular to a sliding direction of the slider.
According to this displacement sensor, the irregular pattern can be formed on the surface of the resistor, without adding filler, carbon fiber, or the like, to the resistor. A stable contact can hence be achieved between the slider and the convex portions formed on the resistor, and accordingly, a stable conduction can be maintained between the slider and the resistor. Therefore, signal noise can be effectively decreased and detection accuracy can be maintained with an elapse of time, and accordingly, durability can be prolonged.